<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Title</title>
</head>
<body>

</body>
<script>
	// - 隐藏内部实现
	// - 不污染外部命名空间
	let a = 100;
	let b = 200;
	(function(){
		let a = 1;
		let b = 2;
	})();
	console.log(a,b);
</script>
</html>